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Introduction

Thu, 01/10/2013 - 21:48 -- abc_admin

Lying in the equatorial South Atlantic, Ascension Island is a UK Overseas Territory and a dependency of the "neighbouring" island of St Helena. Although it is primarily a military base, access has recently improved and the island makes a fascinating destination for seabird enthusiasts. Ascension is a relatively young island of volcanic origin with a hot and usually very dry climate. These conditions have resulted in its flora and fauna being much less diverse than on St Helena. Only some 25 indigenous land plants have been recorded. Ten of these were unique to the island, but four have become extinct (Ashmole & Ashmole 2000). The endemic invertebrates number less than 30 and most of these are tiny inhabitants of crevices in the lava. Just two endemic land birds, the Ascension Rail Atlantisia elpenor (Olson 1973) and the Ascension Night Heron Nycticorax sp.nov.(Ashmole & Ashmole 2000), are known to have existed on Ascension and both are now extinct. Ascension did not have indigenous land mammals, reptiles or amphibians, although the island is an important nesting site for Green Turtles Chelonia midas.

Ascension is, however, a major breeding site for seabirds. The lava plains of the main island originally held huge colonies of Sooty Terns Sterna fuscata, Masked Boobies Sula dactylatra and the endemic Ascension Frigatebird Fregata aquila. Large numbers of Red-footed Sula sula and Brown Boobies S. leucogaster, Brown Anous stolidus and Black Noddies A. minutus, Fairy (White) Terns Gygis alba and both Red-billed Phaethon aethereus and White-tailed Tropicbirds P. lepturus nested in the sea cliffs and stacks. In contrast to the situation on St Helena, petrels were a relatively minor component of the recent seabird community on Ascension with only Audubon’s Shearwater Puffinus lherminieri (now locally extinct) and Madeiran Storm-petrel Oceanodroma castro nesting there.

The island has never had an indigenous human population. It was discovered by the Portuguese in 1501 but has only undergone permanent settlement in the last 200 years. During this period, introduced alien species, particularly cats and rats, have had a serious effect on the native wildlife. The seabirds have been particularly badly affected, with most of the larger species deserting the main island to nest on the predator-free stack of Boatswainbird Island, now the only breeding site of the Ascension Frigatebird Fregata aquila and with a tiny relict population of Red-footed Boobies Sula sula. Audubon’s Shearwater Puffinus lherminieri appears to have been lost entirely. Sooty Terns Sterna fuscata still maintain large colonies on the main island, breeding at intervals of just over nine months rather than annually. Their numbers have, however, been much reduced by cats. Recently, however, a cat eradication programme has been undertaken and is showing signs of success. Masked Boobies Sula dactylatra have bred again on the main island and it is hoped that frigatebirds and the other displaced species will also return. Attempts at more effective rat control are also being made.

Human occupation of Ascension has also resulted in the introduction of five terrestrial bird species: Red-necked Spurfowl Francolinus afer, Common Myna Acridotheres tristis, House Sparrow Passer domesticus, Common Waxbill Estrilda astrild and Yellow Canary Serinus flaviventris. The House Sparrow Passer domesticus arrived as recently as the late 1980s, a small number having been imported to join a solitary individual that arrived accidentally by ship. This population increased initially but never spread beyond the capital, Georgetown. The species went into decline subsequently and may now be extinct on the island. The other three passerines, introduced at a much earlier date, continue to thrive. The francolin population is small and usually secretive but the success of the cat eradication may be reflected in this species being seen more frequently in recent times.

The purpose of this document is to provide a summary of Ascension and its birds for birders interested in the island and potentially planning a visit. The information has been put together from a number of sources and it is intended to add new information as it becomes available. As such, readers are welcome to submit contributions by e-mail to info@africanbirdclub.org.